<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    .damao,
    .ermao {
      width: 200px;
      height: 200px;
      background-color: green;

    }

    /* .damao {
      margin-bottom: 100px;
    }

    .ermao {
      margin-top: 200px;
    } */

    /* 给一个margin 即可 */

    .damao {
      margin-bottom: 200px;
    }
  </style>
</head>

<body>
  <div class="damao"></div>
  <div class="ermao"></div>

</body>

</html>